# -*- test-case-name: twisted.test.test_application -*-
# Copyright (c) Twisted Matrix Laboratories.
# See LICENSE for details.

"""
Plugin-based system for enumerating available reactors and installing one of
them.
"""


from zope.interface import Interface, Attribute, implementer

from twisted.plugin import IPlugin, getPlugins
from twisted.python.reflect import namedAny


class IReactorInstaller(Interface):
    """
    Definition of a reactor which can probably be installed.
    """

    shortName = Attribute(
        """
    A brief string giving the user-facing name of this reactor.
    """
    )

    description = Attribute(
        """
    A longer string giving a user-facing description of this reactor.
    """
    )

    def install():
        """
        Install this reactor.
        """

    # TODO - A method which provides a best-guess as to whether this reactor
    # can actually be used in the execution environment.


class NoSuchReactor(KeyError):
    """
    Raised when an attempt is made to install a reactor which cannot be found.
    """


@implementer(IPlugin, IReactorInstaller)
class Reactor:
    """
    @ivar moduleName: The fully-qualified Python name of the module of which
    the install callable is an attribute.
    """

    def __init__(self, shortName, moduleName, description):
        self.shortName = shortName
        self.moduleName = moduleName
        self.description = description

    def install(self):
        namedAny(self.moduleName).install()


def getReactorTypes():
    """
    Return an iterator of L{IReactorInstaller} plugins.
    """
    return getPlugins(IReactorInstaller)


def installReactor(shortName):
    """
    Install the reactor with the given C{shortName} attribute.

    @raise NoSuchReactor: If no reactor is found with a matching C{shortName}.

    @raise Exception: Anything that the specified reactor can raise when installed.
    """
    for installer in getReactorTypes():
        if installer.shortName == shortName:
            installer.install()
            from twisted.internet import reactor

            return reactor
    raise NoSuchReactor(shortName)
